Duolingo ' is free to use, but you can take a large number of lessons, and it has been attracting attention for its highly gamified system and unique notification messages. Most of Duolingo's ...

Still, those who want an ad-free learning experience can opt to purchase a Duolingo Plus subscription for $6.99 per month, which also allows for offline downloads and supports free education for ...

Language-learning app Duolingo makes around $500 million annually, despite offering all of its lessons for free. WSJ explores how the company is using AI and A/B testing to keep users hooked.